The old Total T4 test (TT4) is no longer considered the best way to test for T4 levels. T4 and T3 can both be bound by other proteins and hormones in the body. When this happens, the T4 or T3 is not usable by the body. The body can only use T4 and T3 that is not bound, or free. For this reason, Free T4, which only tests the free levels of the hormone, is now preferred over Total T4 testing as more accurate.
Do you mean T4, as in thyroid screening
A doctor orders a free T4 blood test (or FT4) to see if your thyroid gland is working properly. The "free" part refers to released thyroxine in your system. The free T4 part actually means it is only measuring the unbound T4 (which is usable) the free T4 blood test is better than just the T4, you need to know how much free T4 (unbound and usable) hormone there is in your body to help determine whether you are suffering from thyroid disease.
The Veterinarian will check a dog's thyroid with blood work, such as a T3, T4 and a TSH test.
T3 is triiodothyronine, and is the active form of the hormone secreted by the thyroid. T4 (thyroxine) is another form of thyroid hormone which must be converted to T3 by your body via the deiodinase enzyme. Although T3 is active, your body produces much more T4. The best way to monitor low thyroid function is by looking at TSH (thyroid stimulating hormone). TSH will be high if the thyroid is not producing enough T3/T4. For the majority of hypothyroid cases, only TSH needs to be monitored. For hyperthyroidism and some hard to treat hypothyroid cases, the doctor will test T3 and T4.
No. A physician must specifically order thyroid function tests, such as a T4 and TSH. (Other specific thyroid tests may be ordered, as well.)
The majority of secreted thyroid hormone is T4 - the storage hormone.
Thyroid stimulating hormone (TSH) stimulates the thyroid gland to produce T4 (Thyroxine).
If my thyroid T4 free blood results are dropping what does this mean?
TSH is the hormone produced by the pituitary gland that tells the thyroid to produce the thyroid hormones T4 and T3.
The hormone that regulates the synthesis and secretion of T3 (Triiodothyronine) and T4 (Thyroxine) by the thyroid gland is thyroid stimulating hormone (TSH) that is produced and secreted by the anterior pituitary gland, also known as the adenohypophysis.
The test for Thyroid Stimulating Hormone (TSH) USED to be considered the gold standard test for thyroid dysfunction. This has changed. Since TSH values only reflect the average of the thyroid's activity over several weeks, doctors now know to test TSH, Free T3 and Free T4 as well as TPOabs to help screen patients for thyroid dysfunction.
Screening thyroid hormone levels regularly includes blood tests for the TSH, T3, T4 and free T4. Normal TSH blood test levels can vary from .3 to 4.5 depending upon gender and life stages; like if you're pregnent or postpartum.